Patent GB-814810-A (GB)
Title: Improvements in or relating to hydraulic servo mechanisms for use in aircraft
IPC: B64C13/24
Filed: 1955-10-25
Abstract: 814,810. Fluid-pressure servomotor control systems. MINNEAPOLIS - HONEYWELL REGULATOR CO. Oct. 25, 1955 [Oct. 25, 1954], No. 30555/55. Class 135. In aircraft flight control apparatus comprising an hydraulic servomotor coupled to move an output member with respect to a manuallyadjustable member and in which the servomotor is controlled by signals from automatic equipment such as an automatic pilot, the servomotor is provided with centering means controlled by the servomotor pressure fluid supply whereby the output member is automatically restored to a selected or neutral position at or near the middle of its range of movement relative to the manually-adjustable member when the pressure fluid supply is withdrawn. As shown, a frame 12, Fig. 1, fixed to the aircraft structure pivotally mounts on a shaft 11 fixed to the frame, an output member 19 connected by a link 25 to the aircraft control surface and a member 10 manually adjustable by a pilot's control lever 13 with or without the help of an hydraulic boost servomotor 17 mounted on the member 10. The member 10 also mounts an hydraulic servomotor 40 controlled by an automatic pilot 45. The shaft 11 includes pressure fluid supply lines 26, 28 and an exhaust line 27 which coact with annular grooves and interconnecting in a sleeve bearing so that at all times there is hydraulic connection between the shaft and the member 10. Under automatic control, signals transmitted by the automatic pilot 45 are received by one or other of solenoids 102, 103, Fig. 3, to operate through a pivoted lever 104, the valve piston 101 of a first control valve 100. The valve piston slides in a movable sleeve 110 subjected to fluid pressure transmitted through a line 70 from the supply line 26 and connected by a pivoted lever 122 to the valve piston 113 of a second control valve 112 having connections 132, 133 to the opposite ends of the doubleacting servomotor 40, exhaust branches 141, 142 connected to exhaust line 27 and a line 140 connected to the pressure line 28. A space 121 to the right of the valve piston 113 is connected by a line 120 to the space between the lands 115, 116 of the valve piston 101 so that on movement of the valve piston 101 the space 121 is connected either to pressure or exhaust. When connected to pressure the valve piston 113 moves the sleeve 110 to follow-up the valve piston 101. When connected to exhaust the sleeve 110 moves to move the valve piston 113. A cut-off valve 145 is interposed between the the valve 112 and the servomotor 40 so that when pressure fluid is being supplied the valve .piston 150 thereof moves rightwardly to first interrupt intercommunication between the opposite sides of the servomotor piston 131 and close branches connected to a line 71 connected with the exhaust line 27 and then connect the supply line 140 so that pressure fluid acts on a piston 155 to quickly move the valve piston 150 against a stop 151. The line 140 is then connected to a line 185 so that pistons 181, 182 urged apart by a spring 184 to lock the piston 131 in its mid-position are forced together to free the piston 131 and at the same time spring- loaded pistons 190, 191 are raised to free the output member 19 from locking engagement with the member 10. Thus, the piston 131 under the control of the automatic pilot 45 is now, through a link 43 pivoted to the output member 19, free to operate the control surface. On pressure fluid being withdrawn from the line 28 either through failure or deliberately by the pilot, the cut-off valve piston 150 moves to the left under the action of its spring so that free communication between the opposite sides of the piston 131 takes place, the pistons 181, 182 lock the piston 131 in mid-position, and the pistons 190, 191 lock the output member 19 to the member 10. The control surface may then be operated by the pilot with or without the aid of boost control. With boost control a crank 15 operates the valve piston 60 of a control valve 16 having connections 63, 64 to the opposite ends of a servomotor cylinder 18, exhaust branches communicating with the exhaust line 71 and a branch. communicating with the line 70 connected to the supply line 26. Valves 73, 80 are interposed between the control valve 16 and the servomotor 70 which together function in a similar manner to the cut-off valve 145. Pressure fluid supplied to the line 70 moving the valve piston 82 of the valve 80 rightwardly against its spring 90 limited by a stop so that pressure fluid acts on the right-hand end of the valve piston 74 of the valve 73 to move this latter valve leftwardly to interrupt communication between the opposite ends of the servomotor cylinder 18. The piston 65 of the servomotor is connected by a link 21 to the fixed frame 12 so that on operation of the control valve 16 the member 10, together with the now locked output member 19, move the control surface. In the event of failure of pressure fluid to the boost servomotor the crank 15 engages stops 320 on the member 10 to mechanically move the control surface, the two sides of the piston 65 now being in free communication with each other. An override valve 161, Fig. 4, interconnecting opposite sides of the servomotor piston 131 is fitted to prevent damage to the linkages when the pilot takes over from automatic control unaware that the control surface is in either of its extreme positions. On overpressure occurring on the left-hand side of the piston 131 a valve piston 170 moves leftwardly and on overpressure occurring on the right-hand side of the piston 131 both the valve piston 170 and a valve piston 164 move leftwardly so that in either case the opposite sides of the piston 131 are interconnected and the member 10 is then free to move. In a modification, the override valve 161 may be replaced by pistons 210, 211, Fig. 5, fitted in a cavity 200 of the rod of the piston 131. In the event of overpressure occurring to the right of the piston 131 both the pistons 210, 211 are moved to the left against normal system pressure supplied through a connection 212 and in the event of overpressure occurring to the left of the 'piston 131 the piston 210 through a passage 215, only moves to the left. In either case the two sides of the piston 131 are interconnected through a passage 221 and ports 220.